Bicarbonate secretion by the rabbit duodenumin vivo:effects of prostaglandins, vagal stimulation and some drugs

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Abstract
Duodenal HCO3‐secretion in anaesthetized rabbits was measured by continuous titration of the recirculating luminal perfusate at pH 7.4. The segment under study started 3–4 cm distal to the pylorus and was devoid of pancreatic and biliary HCO3‐secretion. On histological examination the submucosa was seen to contain Brunner's glands, mainly of a mucous type. Duodenum in rabbit secreted HCO3‐at a considerably higher basal rate (100–125μequiv h‐1cm‐1of intestine) than has previously been found in the rat, cat or dog. The cyclo‐oxygenase inhibitor indomethacin (20 mg kg‐1) reduced the secretion by 30%, while prostaglandin E2(5–80μm, luminal) caused a dose‐dependent increase. Prostaglandins thus seem to be important in regulation of duodenal HCO3‐secretion in the rabbit and may play a role in duodenal protection against acid. Carbachol (1 and 10μg kg‐1) and atropine (0.5 and 1 mg kg‐1) had no effects whereas hexamethonium (to mg kg‐1) caused a persistent decrease (25%) in secretion. Effects of electrical stimulation of the vagal nerves or injection of the alpha2‐adrenergic agonist clonidine markedly depended on the agent used for anaesthesia. In urethane‐anaesthetized animals, clonidine (0.75–75μg kg‐1) tended to increase the secretion whereas with nembutal, clonidine (5–150μg kg‐1) decreased it significantly. Electrical stimulation of the cervical vagal nerves decreased the HCO3‐secretion in urethane‐anaesthetized animals but had no significant effect during nembutal anaesthesia. The responses in the nembutal‐anaesthetized rabbit are similar to those previously observed in the cat, rat or dog.